Lack of postage is just one of several growing problems for election clerks as greater numbers of voters opt to vote by mail. Six out of every 10 Contra Costa voters voted by mail in the last election, the highest rate in the county’s history.

“With the explosion in absentee voting, we are seeing an increase in the number of ballots that we cannot count,” Contra Costa election chief Steve Weir said. “We want every vote to count and if you think about this happening all over the state, it adds up to thousands of uncounted ballots. We need to address the problem.”

Contra Costa County’s rejection rate jumped from 1.3 percent in November 2004 to 1.6 percent in November 2005 to 2 percent in June. In the primary, that translated into 2,472 rejected ballots.

If the trend continues in the much higher turn-out Nov. 7 election, it could reach 4,000 uncounted ballots.

Alameda County doesn’t track its rejection rates but election department spokesman Guy Ashley said they have inserted into the envelope a checklist for voters and a big red reminder note on the outside.

The chief reason election clerks reject ballots is a simple one: They arrive after Election Day.

Others arrive with no signature, the wrong signature or an undecipherable signature.

If you want your vote to count, Weir offers these suggestions:

The mail-in ballot is on two pieces of paper this year, so make sure you include both ballots when you cast your votes.

Sign the envelope. And when you sign the outside of the envelope, take your time and use your standard signature. The clerks must match the signature to your voter registration card but if they can’t read it, your ballot will end up in the rejection pile.

Mail your ballot no later than Friday, Nov. 3. Ballots that arrive after 8 p.m. on Election Day are not counted.

If you fail to mail the ballot on time, just take it to your polling place on Election Day or down to your county’s election office.